Automatic control system



May 5, 1931. R. M. HARDGROVE AUTOMATIC CONTROL SYSTEM Filed Dec. 10,1927 2 Sheets-Sheet l 1 hplqnpl/engorz Rap ar" grove,

by H15 Attornex May 5, 1931. R. M. HARDGROVE 1,804,336

AUTOMATIC CONTROL SYSTEM Filed Dec. 10, 1927 2 Sheets-Sheet 2 Fig 3- Wr'ever' |b| rnoIor effectmg Increase or decrease of combustlble tofurnace orfurnaces.

Inventor-1 Ralph M. Hardgr'ove.

b9 His Attorney.

Patented May 5, 1931 UNITED STATES PATENT OFFICE RALPH M. HARDGIR-OVE,OF BETHLEHEM, PENNSYLVANIA, ASSIGNOR TO BAILEY METER COMPANY, ACORPORATION OF DELAWARE AUTOMATIC CONTROL SYSTEM Application filedDecember 10, 1927. Serial No. 239,201.

This application is a continuation in part of my application, Serial No.125,556, filed July 28, 1926.

The present system relates to automatic control systems wherein changesin the value of a factor which it is desired to maintain at apredetermined value effects adjustments of an operating condition orconditions appurtenant to such factor in a manner to restore the factorto the desired value. An important application of my invention is inconnection with the automatic control of combustion in boiler furnacesand it is this application which I have chosen to specificallyillustrate and describe. It is to be understood, however, that theinvention is not limited necessarily to such application.

In connection with the operation of a boiler furnace or boilerfurnaces-used for generating steam, it is known to provide a controlmeans responsive to an operating condition of the boiler furnace orboiler furnaces, for example, a control means responsive to the steampressure or to the steam flow, and utilize such control means ineffecting adjustment of the fuel and air to the furnace or furnaces soas to supply fuel and air in quantities such as are required to carrythe load on the boiler or boilers. In the operation of a boiler furnaceor boiler furnaces, changes in the steam pressure from a normal valuemay be taken as indicative of changes in the demand for steam, anincrease in steam pressure indicating a decrease in the demand for steamand a decrease in steam pressure indicating an increase in the demandfor steam, and it is the more usual arrangement to make the controlmeans responsive to steam pressure.

A control means of the type referred to is termed usually a mastercontroller or a primary controller, and my invention relates moreparticularly to such a control In the regulation of a boiler furnaceorboiler furnaces by a control means responsive to steam pressure thecondition is met with that when a fuel and air adjustment has been madeby the control means due to a change in steam pressure, a certain timeelapses before the effect of the adjustment is registered on the steampressure. As a result of this,

the difficulty exists that in such a control system there is likely tooccur over-regulation or hunting, which means an unsatisfactoryoperating condition. The object of my invention is to provide animproved control means or master controller for use in a system of theabove re' ferred to type which in a satisfactory manner takes care ofthe operating conditions met with, and for a consideration of what Ibelieve to be novel and my invention, attention is directed to theaccompanying description and the claims appended thereto. In thedrawings,'Fig. l'is a perspective View of a somewhat diagrammatic natureof a control means embodying my invention; Fig. 2 is a detail sectionalview, and Figs. 3 to 9 are diagrammatical views illustrating theoperation of the control means.

Referring to the drawings, 1 indicates a frame provided with arms 2 inwhich is mounted a continuously-rotating shaft 3; also mounted insuitable bearings in the frame is a continuously-rotating shaft 4 and acontinuously-rotating shaft 5. Shaft 4 rotates at a speed slower thandoes shaft 5 and for convenience shaft 4 is referred to as the slowspeed shaft and shaft 5 is referred to as the fast speed shaft. Shafts3, 4 and 5 may be rotated by any suitable means, the only essentialbeing that they be continuously rotated at the desired uniform speed. Inorder to simply the drawing a specific driving means for the shafts isnot shown but instead legends have been applied to the drawing. Inactual practice, the shafts may be driven with advantage by an electricmotor, the mofor being connected to shaft 3 either directly or throughsuitable reduction gearing and shaft 8 being in turn connected to shafts4 and 5 through suitable reduction gearing. Shaft 3 rotates at a speedsubstantially higher than shafts 4 and 5. The directions of rotation ofthe respective shafts is indicated in the drawing by arrows. p Mountedon slow speed shaft 4 are two cir .cuit closers 6 and 7 which may betermed secondary circuit closers and mounted on fast speed shaft are twocircuit closers 8 and 9 which may be termed primary circuit closers.These circuit closers are all alike. Their primary characteristic isthat they are frictionally mounted on the shafts in a manner such thatWhile they tend to turn with the shafts, still they may be turnedrelatively to the shafts when a turning force is supplied to them. Eachcircuit closer comprises a split hub 11 mounted on a sleeve or liner 11*through which the shaft loosely extends, the hub being provided with apair of dependingears 12 through which a bolt 13 extends and by means ofwhich the two parts of the hub may be drawn together to clamp the hub tothe sleeve. The hub is frictionally connected to the shaft by being heldbetween a shoulder 14 fixed on the shaft (see Fig. 2) and a washer 15which is splined on the shaft so as to be free to move axially thereonand which is pressed against the hub by a spring 16 located betweenwasher 15 and a nut 17 on the end of the shaft. By adjusting nut 17 thefrictional connection between the hub and the shaft may be given adesired value. Rigidly connected to hub 11 is an arm 18 provided with anelectrical contact 19 and pivotally mounted on the hub is an arm 20provided with an electrical contact 21 adapted to engage contact 19. Arm20 is biased to a position wherein contact 21 is out of engagement withcontact 19 by a spring 22, the movement of arm 20 being limited by ahead 23 on the end of a bolt 24 which passes loosely through an openingin arm 20 and through spring 22 and is fixed on arm 18.

With the foregoing arrangement, it will be seen that when'contact arm 20of any one of the circuit closers is moved toward the left as viewed inFig. 1, contact 21'will first be brought into engagement with contact 19after which the circuit closer as a whole will be turned on its shaftagainst the action of the friction tending to cause it to rotate withthe-shaft. Primary circuit closers 8 and 9 are provided with stops 25which serve to limit the extent to which the circuit closers may bemoved by shaft 5. Mounted in the path of movement of secondary circuitclosers 6 and 7 are spring return devices each comprising a spring 26located between an ear 27 on the side of frame 1 and a head 28 on theend of a rod 29 which extends through an opening in ear 27. Movement ofrod 29 toward the right is limited by a pin 29. The circuit closers 6and 8 are adapted to be actuated by fingers 30 and 31 fixed on a rod 32mounted to slide in suitable bearing openings in frame 1 and the circuitclosers 7 and 9 are adapted to be actuated by similar fingers 33 and 34carried by a rod 35 which slides in suitable bearing openings inframe 1. The movement of rods 32 and 35 toward the right, as viewed inFig. 1, is limited by a stop 36 fixed on each rod and adapted to engagea wall of frame 1.

Rigidly connected to the right hand end of rod 32 and to one end of aguide rod 37 is a wedge plate 38 having steps on its front surface as isindicated at 39, which terminate at the thick end of the wedge at a flatsurface 39. Wedge plate 38 is pressed toward the right (Fig. 1) bysprings 40 which surround rods 32 and 37, movement toward the rightbeing limited by stop 36 on rod 32 and a similar stop 41 on rod 37.Similarly connected to the right hand end of rod 35 and to one end of aguide rod 42 is a wedge plate 43 having steps on its front face as isindicated at 44 and a flat surface 44 at its thick end. It is pressedtoward the right (Fig. l) by springs 45 which surround rods 35 and 42,the movement toward the right being limited by the stop 36 on rod 35 anda similar stop 46 on rod 42. As will be seen from Fig. 1, and also as isclear from the diagrammatic view, Fig. 3, wedge plates 38 and 43 areoppositely arranged, their inclined surfaces crossing each other midwaybetween their upper and lower ends when the wedge plates are in theirextreme right hand positions.

l/Vhen wedge plate 38 is moved toward the left (Fig. 1) rods 32 and 37will be moved with it, the rods sliding through the bearing openings inthe frame. Finger 30 will engage arm 20 of circuit closer 6 and move itto bring its contact 21 into engagement with its contact 19 after whichcircuit closer 6 will be turned as a whole on shaft 4 and in acounter-clockwise direction as viewed in Fig. 1. Also, finger 31 willengage arm 20 of circuit closer 8 and move it to bring its lar mannerwhen wedge plate 43 is moved to- Ward the left.

Wedge plates 38 and 43 are moved by a cam 47 fixed oncontinuously-rotating shaft.

3, which cam operates through the intermediary of a fiat plate 48 andtwo pins 49, one for each wedge plate. Plate 48 is carried by two guiderods 50 which slide in bearing openings in frame 1 and it is pressedtoward the edge of the cam by springs 51 which surround the guide rods.On plate 48 is a roller 52 against which cam 47 operates. Cam 47 has asteep portion a followed by a portion 7) which increases slightly inheight beginning at the point where it joints portion a and finallyterminates in a small projection 0 followed by a rapidly receding porbean amount of an order equal to two steps on wedges 38 and 43. With thisarrangement, it will be seen that when cam 47 r0- tates and beginningwith the cam in the position shown in Fi s. 1 and 3, plate 48 is firstpushed to the le t by steep cam portion a after which it ismoved slowlyfurther toward the left while cam portion 7) passes by roller 52 andthen finally it is given a small further movement toward the left byproj ection c after which it is permitted to return to its formerposition, following along cam portion d. When plate 48 moves toward theleft, pins 49 are forced against wedge plates 38 and 43 thus moving saidwedge plates toward the left to effect operation of certain of thecircuit closers, 6, 7, Sand 9 depending on the position of pins 49relative to the front surfaces of wedges 38 and 43.

Pins 49 are moved up and down relatively to the surfaces of wedge plates38 and 43 in accordance with the operating condition of the boiler orboilers to be controlled, and in this case taken to be the steampressure. To this end they are shown in the present instance as beingfixed to the end of an arm 53 connected to a rotatably-mounted shaft 54to which is connected a known type of Bourdon tube 55 the interior ofwhich is connected by a pipe 56 to the steam conduit which conveys steamfrom the boiler or bank of boilers being controlled. The arrangement'issuch that when the stem pressure increases, Bourdon tube 55 straightenssomewhat thereby turning shaft 54 in a directionto raise pins 49relatively towedge plates 38 and 43 While when the steam pressuredecreases, Bourdon tube 55 contracts thereby turning shaft 54 in adirection to lower pins 49 relatively to wedge plates 38 and 43. Theextreme movements of pins 49 are limited by suitable stops against whicharm 53 engages, such stops being indicated at 57 in Fig. 1. The Bourdontube arrangement is shown only diagrammatically and it is to beunderstood that any suitable arrangement for accomplishing the desiredresult may be used.

The arrangement is such that when the desired normal steam pressureobtains, pins 49 stand midway between the ends of the wedge plates as isshown in Figs. 1 and 3.

The control means or master controller as illustrated in Fig. 1 may beused in connection with any suitable automatic boiler furnace controlsystem. For example, it may be used in a system such as that disclosedin the application of Erwin G. Bailey, Serial No. 749,769, filedNovember 13, 1924. When utilized in a boiler furnace control system thearrangement is such that the one pair of circuit closers, for instance,circuitclosers 6 and 8, whenever either is closed, serve to efiect anadjustment or adjustments in a direction to decrease the rate of supplyof a combustible or combustibles being fed to the'furnace or furnaces,and the other pair of circuit closers 7 and 9, whenever either is closedserve to effect an adjustment or adjustments in a direction to increasethe rate of supply of combustible or combustibles being fed to thefurnace or furnaces. In either case, the extent of the adjustmentsvaries in amount directly-with the length of time the contacts are heldclosed. The specific arrangement used for adjusting the rate of supplyof a combustible or combustibles to the furnace or furnaces forms nopart of my present invention. Suitable arrangements are now known.Accordingly, I have indicated what may be taken as a suitablearrangement by the reversible electric motor 58 (Fig. 3) it beingunderstood that when motor 58 operates in one direction it effects anadjustment or adjustments in a direction to decrease the rate of supplyof a combustible or combustibles to the furnace or furnaces while whenit operates in the other direction, it effects an adjustment oradjustments in a direction to increase the rate of supply of acombustible or combustibles to the furnace or furnaces. In thisconnection ilfiS to be understood that by the term combustible I referto fuel (such as coal oil or the like) to air, or to both. Asillustrated in Fig. 3 connected to and driven by the motor 58 throughthe medium of gearing 101 is a damper 109 capable of being positioned inthe duct 102 to vary the flow of a combustible therein.

The'two circuits for motor 58 are controlled by relays 59 and 60. Whenrelay 59 is energized its armature 61 is moved into engagement withrelay contact 62 thereby connecting motor 58 directly to supply lines 63through conductors 64 and 65 to effect operation of motor 58 in adirection to increase the rate of supply of combustible or combustibles,and when relay 60 is energized its armature 66 is moved into engagementwith relay contact 67, thereby connecting motor 58 directly to supplylines 63 through conductors 64 and 68 to effect operation of motor 58 ina direction to decrease the rate of supply of a combustible orcombustibles. The circuits for relays 59 and 60 are interconnected sothat when one relay is energized the circuit for the other relay isopened. The circuit for relay 59 may be traced as follows: upper supplyline 63, conductor 69, either of the circuit closers 7 or 9 which areconnected in parallel, conductor 70, winding of relay 59, back contact71 of relay 60 and conductors 72 to lower supply line 63. The circuitfor relay 60 may be traced as follows: upper supply line 63, conductor69, either of the circuit closers 6 or 8 which are connected inparallel, conductor 73, winding of relay 60, back contact 74 of relay 59and conductor 72 to lower supply line 63. It will thus be seen that thecircuit for relay 59 includes the back contact 71 of relay 60 and thecircuit for relay 60 includes the back contact 74 of relay the controldevice is obtained if relative nu merical values are considered for thespeeds of rotation of shafts 3, 4 and 5. Accordingly, values which Ihave found to be satisfactory in actual use are given. It is to beunderstood, however, that this is only by way of example and is not tobe taken as a limitation of my invention.

Shaft 3 may be revolved at a speed of the order of eight revolutions perminute so that cam 47 makes a complete revolution about every eightseconds. This means that durmg each eight seconds plate 48 is movedbythe oam to bring pins 49 into engagement with wedges 38 and 43, forcingboth wedges toward the left a distance depending upon the location ofpins 49 relative to the, wedges and moving one or more of the circuitclosers 6, 7, 8 and 9 relatively to shafts 4 and 5. Slow speed shaft 4may be rotated at a speed of the order of one revolution in four hundredminutes, and fast speed shaft 5 may be rotated at a speed of the orderof one revolution in one hundred thirty-five minutes. This'means thatwhile shaft 3 is making a complete revolution, shaft 4 makes about1/3000 of a revolution and shaft 5 makes about 1/1000 of a revolution.The maximum movement of circuit closers 6 and 8 relative to shafts 4 and5 is obtained when pin 49 engages the flat surface 39 of wedge plate 38and the maximum movement of circuit closers 7 and 9 relative to shafts 4and 5 is obtained when pin 49 engages the flat surface 44 of wedge plate43.. Under these circumstances, circuit closers 6 and 7 may be movedrelatively to shaft 4 through a total angle of the order of 14 andcircuit closers" 8 and 9 may be moved relatively to shaft 5 through atotal angle of the order of 7. Fingers 31 and 34 are arranged relativelyto circuit closers 8 and 9 so that (starting from the positio ns shownin Fig. 3) on the first or initial rotation of cam 47 fingers 30 and 33will" have moved circuit closers 6- and 7 through an angle of about 7before fingers 31 and 34 begin to move circuit closers 8 and 9. Thequick return devices comprising springs 26 and heads 28 are arranged sothat they are enga ed and compressed by circuit closers 6 and *7 duringabout the last 2 of the movement of each circuit closer.

When the steam pressure in the steam conduit or header for the boiler orbank of boilers it at its normal value, pins 49 stand midway between theupper and lower ends of wedge plates 38 and 43 as shown in Fig. 3. Whenthe pressure increases it is assumed that the pins move upward and whenthe pressure decreases it is assumedthat they are brought into line withflat surfaces 39 or 44. During the operation of cam 47, ins

49 are periodically clamped between p ate 48 and the-surfaces of wedgeplates 38 and 43 and again released. VVhenreleased, the.

pins are free to assume a position corresponding to the steam pressure.Shaft 53 has sufficient flexibility in an axial direction to permit ofthe pins when clamped between plate 48 and wedge plates 38 and 43,moving with the plate. If the steam pressure changes at a time when thepins are clamped between the plate 48 and the wedge plates, the Bourdontube 55 may take the distortion.

Fig. 3 shows diagrammatically the positions of the various parts whenthe steam pressure is at normal value and before cam 47 has made arevolution, it being assumed that circuit closers 8 and 9 have beenbrought into engagement with stops 25 and that circuit closers 6 and 7have been brought into engagement with fingers 30 and 33. Pins 49 standmidway between the upper and lower ends of wedge plates 38 and 43. Whencam 47 turns in the direction indicated by the arrow in Fig. 3, plate 48is moved fairly rapidly toward the left by cam section a first bringingpin 49 into engagement with wedge plates 38 and 43, and then effectingmovement of the wedge plates toward the left. The movement of the wedgeplates. toward the left is then continued slowly by portion 5 of cam 47and is given a final push toward the left by the small projection c onthe cam. Following this, the wedge plates are permitted rapidly toreturn to their initial positions by the receding portion d of the cam.The arrangement i's'such that under these conditions'circuit closers 6and 7 will have been closed and in addition to that moved in acounter-clockwise direction on shaft 4 a distance of about 7. Circuitclosers 8 and 9 will not have been affected as fingers 31 and 34 arespaced from them a distance such that they will not quite have reachedthese circuit closers. The positions of the parts at the time projection0 engages plate 48 is illustrated in Fig. 4.

As soon as contact fingers 30 and 33 move away from the circuit closers6 and 7 the circuit closers open immediately and begin to movevery'slowly back toward their initial positions being carried along byslow speed shaft 4. Before they will have'moved far, however, cam 47will have again operated to force wedge plates 38 and 43 toward theleft. On this second'operation of the camnothing will happen except thatcircuit closers 6 and 7 will be momentarily closed by the projection 0and will be moved again relatively to shaft 4 a distance correspondingto that which they have been carried around by shaft 4 during the timethey have been released by fingers 30 and 33. In view of the fact,however, that shaft 4 makes but about 1/3000 of a revolution while shaft3 makes 1 revolution, it will be clear that circuit closets 6 and 7 willhave been carried back but a very short amount, and an amount aboutequal to that which they were moved initially by cam projection 0.

When the control device is in operation, cam 47 rotates continuously. Vhat may be considered the normal positions of the circuit closers whenthe steam pressure is at normal value is substantially their positions,as shown in Fig. 4, circuit closers 8 and 9 being held by their stops 25and circuit closers 6 and 7 being operated on by fingers 30 and 33 atthe extreme end of their movements as described in the precedingparagraph.

It will thus be seen that as cam 47 continues to rotate, assuming pins49 remain in the same position, cam projection 0 causes repeatedsubstantially simultaneous closings Y of circuit closers 6 and 7 but ofVery short duration. Each time circuit closers 6 and 7 close eitherrelay 59 or relay 60 will'be energized tending to operate motor 58 ineither one direction or the other. The two relays are set alike and asonly one can operate at a time because their circuits areinterconnected, it results in actual practice that over a period of timeeach is operated about the same number of times. The net effect is thatthe continuous simultaneous closing of the circuit closers 6 and 7results in no appreciable adjustment of motor 58 in either direction.

Assume now that the system is in operation, motor 58 being connected tooperate and representing the controlled mechanism and cam 47 and shafts4 and 5 being in operation. Assume also that the steam pressure is atnormal value so that pins 49 stand in the central positions shown inFig. 4. Under these circumstances, .as just explained, circuit closers 6and 7 will be closed simultaneously at regular intervals for an instantbut will have no appreciable effect on motor 58. Assume now that thereis an increase in the steam pressure which indicates a decrease indemand for steam and hence re quires that the rate of supply ofcombustible or combustibles to the furnace or furnaces be decreasedsomewhat. Increase in steam pressure causes pins 49, when released byplate 48 to be raised by Bourdon tube a certain distance so that whenthe pins are again moved forward by cam 47 and plate 48, the one pin 49will engage its wedge plate 38 at a higher step on the stepped wedgesurface 39 and the other pin 49 will engage its plate 43 at a lower stepon the stepped wedge surface 44. This is illustrated in Fig. 5.

7 As a result, wedge plate 38 will be moved in advance of wedge plate43. Also, wedge plate 38 will be moved a greater distance than beforewhile wedge plate 43 will be moved a lesser distance than before'Because of this, the movement of wedge plate 38 will be sufficient toeffect the closing of both circuit closers 6 and 8 while on the otherhand, the movement of wedge plate 43 now will not be sufficient toeffect the closing of circuit closer 7 because during one revolution ofcam 47 circuit closer 7 will not have been carried back by rotatingshaft 4 a distance suflicient to make up for the lesser. amount whichwedge plate 43 is moved. Assuming the pressure has changed enough tomove pins 49 several steps along the wedges as is shown in Fig. 5, thenthe circuit closers 6 and 8 will be. oids kd by cam portion a and willbe held closed while cam portions 6 and 0 are effective. The closing ofcircuit closers 6 and 8 closes the circuit of relay 60, effectingoperation of motor 58 in a direction to decrease the rate of supply ofcombustible or combustibles to the furnace or furnaces.

As soon as the portion (1 of' cam 47 is reached wedge plates 38 and 43start back toward their initial positions, releasing circuit closers 6and 8. Both circuit closers will open immediately, thus opening thecircuit on relay 60 and stopping motor 58. Also both circuit closerswill be carried back toward their former positions by the rotation ofshafts 4 and 5, the circuit closer 8 being carried backmore rapidly onaccount of the faster turning of shaft 5. On the next rotation of cam 47(and assuming the steampressure remains at the new value) circuitclosers 6 and 8 will be again engaged and closed, the circuit closer 8being engaged first because it will have been moved back further by therotation of its shaft 5 than will circuit closer 6'by the rotation ofits shaft 4. The arrangement is such that circuit closer 8 will havebeen carried back during the interval it is released an amount justslightly more than that which it was moved by cam portion 0. On thisnext revolution of cam 47, therefore, circuit closer 8 will be engagedand closed by cam portion 6 just in advance of cam portion 0 and will beheld closed until portion 0 has moved past it, the circuit closer beingat the same time again turned on its shaft in a counter-clockwisedirection. During the interval circuit closer 8 is closed, whichinterval is of short duration, a small additional adjustment of motor-58in a direction to decrease the rate of supply of combustible orcombustibles to the furnace or furnaces will take place. If as .a resultof the initial adjustment or the initial adjustment followed by one ormore repeat adjustments of short duration the steam pressure stopsincreasing and starts to return toward normal value, then pins 49 willmove back toward their former positions and no further adjustment willtake place in this direction. On the other hand, if, following the firstadjustment referred to above, the steam pressure continues to risebringing the pins 49 to a still higher step on wedge plate 38 and astill lower step on wedge plate 43 then circuit closers 6 and 8 will beagain closed after the manner just described to effect a furtheradjustment or adjustments of motor 58. Fig. 5 illustrates a condition ofoperation wherein pins 49 have been raised a number of steps by increasein steam pressure and as will be noted circuit closers 6 and 8 areboth-closed.

Assume now that the pressure continues to rise bringing the one pin 49into line with flat surface 39 Under these circumstances, the maximumturning movement is imparted to circuit closers 6 and 8, circuit closer6 being brought into engagement with the springpressed head 28 and thespring being compressed during the latter part of the movement, forexample the last 2 degrees of movement. This is illustrated 'in Fig. 6.

As a result of this as soon as finger 30 re leases circuit closer 6, itis moved back by the spring-pressed head 28 through 2 degrees. Now whencam 47 makes another revolution, circuit closer 6 will be closed whilebeing moved through a distance represented by thatwhich it is returnedby thespring device plus the small amount which it was carried back dueto the rotation of shaft 4. This represents an appreciable time and itwill effect a predetermined adjustment of motor 58. Thus it will'be seenthat when the steam pressure has varied a predetermined amount,

there will be a substantial constant adjustment of motor 58 for eachrevolution of cam 47.

In connection with the spring pressed head 28, the arrangement is suchthat it begins to become effective as the pin 49 reaches the step on thewedge adjacent to the flat portion 39 and becomes fully eflective'assoon as the flat portionis reached. Thus when the pressure has varied apredetermined amount, the

spring pressed head begins to be effective and increases in its "actionuntil when pin 49' reaches the flat portion 39 the action becomes amaximum.

Assume now that the steam pressure having reached a maximum value asshown in Fig. 6,

adjustments have taken place to such an extent that the furnace hasresponded and the steam pressure begins to decrease. Assume also that ithas decreased until pins 49 have reached the position shown in Fig. ,7,this being a position about the same as that which they occupied inFig.'5.- Now when cam 47 moves forward wedge plate 38 will be operated alesser amount than previously. 'As aresult of this, neither circuitcloser 6 nor circuit closer 8 will be closed because of the fact thatthey have not had time to be carried back by rotating shafts 4 and 5 an:amount equal to the decrease in the movements of wedge plate 38. On theother hand, wedge plate 43 will be moved a distance greater than beforeand a distance such that its finger 33 will engage and close circuitcloser 7. This is due to the fact that during the previous period ofoperation, circuit closer 7 has been carried by its shaft back to theregion in which finger 33 was previously moving. In this connection itis to be noted that since circuit closer 7 has no stop, it will be movedback continuously by shaft 4 as long as it is not engaged by finger 33.As a result, therefore, circuit closer 7 will be closed and effectoperation of motor 58 in a direction to increase the rate of supply ofcombustible or combustibles to the furnace or furnaces. By this means,the rate of decrease of the steam pressure is checked, so to speak; thatis to say, forces are put into operation tending to been effected, thepressure is moving back to ward normal, adjustments in the oppositedirection are effected to prevent a too rapid return of the pressuretoward normal, (a thing likely to result in the pressure passing be-'yond normal in the other direction) is an important feature of myinvention. By it the I result is obtained that as the pressure returnstoward normal, the rate of return as the pressure approaches normal isgradually decreased so that when normal pressure is reached the rate ofreturn approaches zero which means that the pressure will not go beyondor will have a tendency not to go beyond normal in the other direction.v

The cycle of operatiorris illustrated by the diagram in Fig. 9 whereinthe straight line A-B represents normal ressure and the line Crepresents a curve f0 lowed by the steam pressure in departing from andreturning again to normal. Beginning at a point D where the steam;pressure is normal and following line C it will be seen that the steampressure is increasing quite rapidly. As a result circuit closures -6and 8 will be actuated upon successive revolutions of cam 47 after themanner already described to effect successive adjustments of motor 58 ina d1- rection to decrease the rate of supply of combustible orcombustibles to the furnace or furnaces. During this period'circuitclosers 7 and 9 will not be closed since circuit closer 9 is held by itsstop 25 andcircuit closer 7 is located in a region not now reached byfinger 33 upon successive actuations of wedge plate 43. However, circuitcloser 7 will be traveling back slowly toward finger 33 due to therotation of shaft 4.. At point E the steam pressure, due to theadjustments which have been made, ceases to rise and is about to turnback toward normal. At this point there will be successive actuations ofthe wedge plates upon the same step which as already explained resultsin the closing of circuit closers 6 and 8 for very short periods, thecircuit closer 8 being closed for the longer period and effecting smalladjustments of motor 58 in a direction to decrease the rate ofcombustible supply. The pressure now starts back toward normal and atpoint F for eX- ample, the pins 49 will have lowered to a point on thewedge plates such that the movement of wedge plate 38 is decreased to anextent that fingers 30 and 31 do not reach circuit closers 6 and 8 whilethe movement of wedge plate 43 is increased to an extent such thatfinger 33 does reach circuit closer 7 and effects a long closure of it.Circuit closer 7 is in a position to be reached by finger 33 becauseduring the periodof increasing presv sure it has been traveling backcontinuously with shaft 4. The closing of circuit closer 7 will effectan adjustment of motor 58 in a direction to increase the rate ofcombustible supply even though the steam pressure is still well abovenormal. As a result, therefore, there is a tendency to retard the rateof approach of the steam pressure toward normal. Retarding adjustmentsof motor 58 will continue as the steam pressure continues to decrease.At point G it is assumed that the decrease in the steam-pressure hasbeen checked definitely and that it tends now to increase slightly asindicated at point H and to become stabilized at this point. This mayhave been due, for example, to a small change in load on the boiler orboilers causing a small change in pressure. Under these circumstances,circuit closer 7 will be closed and also the circuit closers 6 and 8.However, since circuit closer 8 is on the fast speed shaft 5 it will bereturned further during a revolution of cam 47 than will either of thecircuit closers 6 and 7. Circuit closer 8 will be closed firsttherefore, and will be the controllng circuit closer out of the three.It will effect small adjustments of motor 58 in a direction to decreasethe rate of supply of combustible thus again turning the pressure towardnormal but at a slow rate. Beyond point H the pressure is indicated asapproaching normal gradually and when normal pressure is reached furtherdecrease in pressure may cease. However, in some instances the decreasein pressure may not cease when normal pressure is reached and at point Iit is indicated as having passed slightly beyond normal. When t ishappens, circuit closer 9 (and also circuit closer 7) will be closed toeffect an adjustment of motor 58 in a direction to increase the rate ofcombustible supply and turn the pressure back toward normal. And ifthepressure then moves back above normal as is indicated at Jfthen circuitcloser 8 (and also circuit checked at the point G on its downwardjourney there would be a tendency for it to become stabilized at thispoint were it not for the arrangement of the circuit closers on the slowand fast shafts. At this time circuit closers 6, 7 and 8 were beingclosed but since circuit closer 8 was on fast shaft 5 while circuitclosers 6 and 7 were on the slow shaft, circuit closer 8 became thecontrolling circuit closer of the three and gave the control a definiteturn toward normal value again.

This condition of operation is illustrated in Fig. 8, where it will beseen that circuit closers 6 and 7 are both positioned so they are'beingclosed by fingers 30 and 33, and that circuit closer 8 is also beingclosed by finger 31. On the other hand, however, circuit closer 9 is notbeing closed because it is held by its stop 25 out of range of thefinger 34.

In the foregoing description of the operation a condition of increasingsteam pres sure was assumed. Upon decrease in steam pressure whichindicates increase in the demand for steam, the operation is similar tothat described, except that it takes place in opposite directions.

In accordance with the provisions of the patent statutes, I havedescribed the principle of operation of my invention, together with theapparatus which I now consider to represent the best embodiment thereof,but I desire to have it understood that the apparatus shown is onlyillustrative and that the invention may be carried out by other means.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is

1. A control system for use with heating apparatus having a factorappurtenant to the heating apparatus which, during operation of theapparatus, tends to vary from a predetermined value for maintaining saidfactor at the predetermined value, comprising means positioned inaccordance with variations of said factor from the predetermined value,means which when operated tends to restore said factor to itspredetermined value, and control means through which said firstnamedmeans effects operation of said secondnamed means, said control meanscomprising mechanism for effecting movements of said second-named meansin each direction, means whereby as said factor approaches itspredetermined value after having departed from such value, saidmechanism will be operated to effect movement of said second-named meansin a direction tending to cause departure of said factor from itspredetermined value and in amounts depending upon the rate at which suchfactor is approaching its predetermined value whereby as the factorapproaches its predetermined value its rate,

of approach will be decreased.

2. A control system for use with heating apparatus having a factorappurtenant to the heating apparatus which, during operation of theapparatus, tends to vary from a predetermined value for maintaining saidfactor at the predetermined value, comprising means positioned inaccordance with variations of said factor from the predetermined value,means which when operated tends to restore said factor to itspredetermined value, control means through which said first-named meanseffects operation of'said second-named means, said control meanscomprising mechanism for effecting movements of said secondnam'ed meansin each direction, means whereby as said factor approaches itspredetermined value after having departed from such Value, saidmechanism will be operated to effect movement of said second-named meansin a direction tending to cause departure of said factor from itspredetermined value whereby as the factor approaches its predeterminedvalue its rate of approach-will be decreased, and means which serves toprevent said factor from becoming stabilized at a value other than thepredetermined value.

3. A master controller comprising contact means which when actuatedserves to effect an operation in one direction, contact means which whenactuated serves to effect an operation in the other direction, meanstending to rotate said contacts in one direction, an actuator for eachcontact which when moved into engagement with its contact turns saidcontact in a direction opposite to that in which it tends to rotate,each actuator comprising a wedge-shaped member, the two wedge-shapedmembers being oppositely-arranged, and means adapted to engage bothactuators to move them simultaneously.

.4. A master controller comprising two sets of contacts, means tendingto rotate one set of contacts at a'given rate and in a given direction,means tending to rotate the other set of contacts at a different ratebut in the same direction, actuators for effecting closing of said setsof contacts androtation of them in a direction opposite to said givendirection, and movable means which is positioned to move said actuatorsvariable distances.

. 5'. A control system for use with heating apparatus having a factorappurtenant to the heating apparatus which, during operation of theapparatus, tends to vary from a predetermined Value for maintaining saidfactor at the predetermined value, comprising reversible mechanism whichwhen operated effects changes in said factor, electric contact meanswhich when actuated effects operation of said reversible mechanism inone direction, electric contact means which when actuated effectsoperation of said reversible mechanism in the other direction, awedge-shaped actuator for each contact means, said actuators beinglocated side by side with the wedges oppositely disposed, and means formoving said wedge-shaped actuators comprising a member which ispositioned in accordance with the value of said factor.

6. In a boiler control system, reversible mechanism for regulating thesupply of.combustible or combustibles to a boiler installation, a set ofprimary contacts, a set of secondary contacts, each set comprising acontact for effecting operation of the reversible mechanism in eachdirection, means which tends to rotate continuousuly said sets of contacts but at different speeds, actuators for said contacts, and meansresponsive to an operative condition of the boiler installation formoving said actuators.

7 In a boiler control system, reversible mechanism for regulating thesupply of combustible or combustibles to a boiler installation, meansresponsive to" an operating condition of the boiler installation foreffecting operation of said mechanism to increase or decrease the rateof combustible supply to the installation, and means whereby when aftera departure from normal operating condition, normal operating ,conditionis again approached, said reversible mechanism is operated in adirection tending to again effect departure from normal operatingcondition whereby the approach toward normal operating condition isretarded.

8. In a boiler control system, reversible mechanism for regulating thesupply of combustible or combustibl'es to a boiler installation, meansresponsive to pressure of vapor generated in said installation foroperating said reversible mechanism to increase the combustible supplyupon decrease in vapor pressure and to decrease the combustible supply uon increase in pressure, and means where y after said mechanism has beenoperated upon a departure of the pressure from normal value to cause thepressure to return toward normal value said mechanism will be operatedin a direction tending to again cause the pressure to depart from normalvalue whereby the approach of the pressure toward normal value will beretarded.

9. In a control system, the combination of a reversible mec anism,electric contactment of said mechanism in one direction, electriccontact means which when actuated effects movement of said mechanism inthe other direction, means for actuating said contacts simultaneouslycomprising oppositely arranged, overlapping, wedge shaped,

members, and means for preventing said contacts from being connectedsimultaneously to said reversible mechanism.

10. In a control system, the combination of a reversible mechanism,electric contact means which when actuated effects movement of saidmechanism in one direction, electric contact means which when actuatedeffects movement of said mechanism in the other direction, means foractuating said contacts simultaneously comprising oppositely arranged,overlapping, wedge shaped members, and interlocking relays forpreventing said contacts from being connected simultaneously to saidreversing mechanism.

11. In a control system, the combination of a reversible mechanism,electric contact means which when actuated effects movement of saidmechanism in one direction, electric contact means which when actuatedeffects movement of said mechanism in the other direction, oppositelyarranged, overlapping, wedge shaped members which when moved effectclosing of said-electric contact means, means which engages both saidwedge shaped members to move the same, said means being movablerelatively to said members, and a continuously rotating cam forimparting periodic movement of said last named means.

12. In a control system, the combination of a reversible mechanism, acontinuously rotating shaft, contacts mounted on said shaft infrictional engagement therewith whereby the contacts tend to turn withthe shaft but may be moved relatively to the shaft, oppositely arranged,overlapping, wedge shaped members which when moved close said contactsand turn them relatively to the shaft and in a direction opposite tothat in which the shaft rotates, and means movable relatively to theinclined surfaces of said wedge shaped members which engages the wedgeshaped members and moves them ina direction to close said contacts.

13. In a control system, the combination of a reversible mechanism, acontinuously rotating shaft, contacts mounted on said shaft infrictional engagement therewith whereby the contacts tend to turn withthe shaft but may he moved relatively to the shaft, oppositely arranged,overlapping, wedge shaped members which when moved close said contactsand turn them relatively to the shaft and in a direction opposite tothat in which the shaft rotates, means movable relatively to theinclined surfaces of said wedge shaped members which engages the wedgeshaped members and moves them in a direction to close said contacts, andmeans for preventing said contacts from being connected simultaneouslyto said reversible mechanism.

14. In a control system, the combination of a reversible mechanism,electric contact means which when actuated effects movement of saidreversible mechanism in one direction, electric contact means which whenactuated effects movement of said mechanism in the other direction, acontinuously rotating shaft to which said contact means are frictionallyconnected and which tends to turn them in one direction, a secondcontinuously rotating shaft which turns at a speed different from thatof the first named continuously rotating shaft, secondary electriccontact means frictionally connected to said second continuouslyrotating shaft, said secondary electric contact means being connected inparallel with said primary electric contact means, and periodicallyactuated means which tends to close said contacts and rotate them in adirection opposite to that in which the shafts tend to rotate.

15. A control system for use with apparatus having a factor which,during operation of the apparatus, tends to vary from a predeterminedvalue, for maintaining said factor at the predetermined value,comprising adjustable means which when operated tends to restore saidfactor to its predetermined value, control means for effecting movementsof said adjustable means, means responsive to the rate of departure ofthe factor from the predetermined value, said last-named means effectingvariations in the magnitude of said movements, and selective meansefiective as said factor approaches the predetermined value after havingdeparted from such value for operating said control means to effectmovement of said adjustable means in a direction tending to causedeparture of said factor from its predetermined value and in amountsdepending upon the rate at which said factor is approaching itspredetermined value whereby as the factor approaches its predeterminedvalue its rate of approach will be decreased.

16. A control system for use with apparatus having a factor which,during operation of the apparatus, tends to vary from a predeterminedvalue, for maintaining said factor at the predetermined value,comprising means positioned in accordance with variations of said factorfrom the predetermined value, adjustable means which when operated tendsto restore said factor to its predetermined value, control means throughwhich said first-named means effects operation of said adjustable means,said control means comprising mechanism for effecting movements of saidadjustable means in each direction, means responsive to the rate ofdeparture of the factor from the predetermined said adjustable means ina direction tending to cause departure of said factor from itspredetermined value and in amounts depending upon the rate at which saidfactor is approaching its predetermined value whe'reby as the factorapproaches its predetermined value its rate of approach will bedecreased.

17. A control system for use with apparatus having a factor which,during operation of the apparatus, tends to vary from a predeterminedvalue, for maintaining said factor at the predetermined value,comprising adjustable means which when operated tends to restore saidfactor to its predetermined value, control means for effecting movementsof said adjustable means, means responsive to the rate of departure ofthe factor from its predetermined value, said last-named means effectingvariations in the magnitude of said movements, means effective upondeparture of said factor a predetermined amount from the predeterminedvalue and limiting the successive movements of said adjustable means toa constant magnitude, and selective means effective as said factorapproaches its predetermined value after having departed from such valuefor operating said control means to effect movement of said adjustablemeans in a direction tending to cause departure of said factor from itspredetermined value and in amounts depending upon the rate at which saidfactor is approaching its predetermined value whereby as the factorapproaches its predetermined value its rate of approach will bedecreased.

18. A control system for use with apparatus having a factor which,during operation of the apparatus, tends to vary from a predeterminedvalue, for maintainig said factor at the predetermined value, comprisingmeans positioned in according with variations of said factor from thepredetermined value, adjustable means which when operated tends torestoresaid factor to its predetermined value, control means throughwhich said first-named means effects operation of said adjustable means,said control means comprising mechanism for effecting movements of saidadjustable means in each direction, means responsive to the rate ofdeparture of the factor from the predetermined value, said lastnamedmeans effecting variations in the magnitude of said movements, meanseffective upon departure of said factor a predetermined amount from thepredetermined value and limiting the successive movements of saidadjustable means to a constant magnitude, and selective means effectiveas said factor approaches the predetermined value after having departedfrom such value for operating said control means to effect movement ofsaid adjustable means in a direction

